The neurological effect of concussions and other serious head trauma in sports is, of course, a topic of considerable interestto scientists, as well as to athletes and, for younger players, their parents.

But there has been less attention paid to the potential effects of so-called preconcussive impacts, or more minor hits to the head, like those that might be sustained when someone heads a soccer ball. A 2011 brain-scan study of experienced, adult soccer players found subtle structural changes in certain parts of the brain that might be associated with repeated slight impacts.

But it has been difficult to measure the actual cognitive functioning of soccer players right after they have been heading the ball, in part because the equipment required is complicated or lab-based.

Then came the iPad, with its simple, intuitive touch-screen and portability.

“We had been trying for some time to develop a very simple test” of cognition, said Anne B. Sereno, a professor of neurobiology at the University of Texas Health Science Center in Houston, who led the new study.

So Dr. Sereno and her colleagues developed an iPad version of a well-accepted cognitive test, in which volunteers are told to focus on an image of four boxes grouped in a roughly square shape on the screen.

In one part of the test, the volunteers are asked to touch a box when it lights up on screen.

In another, more demanding, task they are asked to ignore the box that glows and instead touch the box immediately opposite from the lit box. This second task, known as the anti-point response, tests how well volunteers can control their reactions and impulses and intellectually override a natural response — the impulse to look at and reach for the lit box — and correctly touch its opposing counterpart.

The anti-point response “is a good test of executive function” in the brain, Dr. Sereno said.

Next, she and her colleagues recruited a girls’ high school varsity soccer team in the Houston area.

The team was female, because “female soccer players are second only to football players in the number of concussions” that they develop each year, Dr. Sereno said, suggesting that head trauma is a common problem in the sport. Girls are also more likely than boys to sustain injuries during soccer heading, some statistics show.

But whether normal, everyday soccer heading was, potentially, having an impact on the girls’ ability to think was unknown.

Dr. Sereno and her colleagues brought their iPads to the field and waited for the team to finish a varsity practice, during which each girl repeatedly headed the ball, some as many as 20 times.

The scientists also had recruited a group of 12 non-soccer playing high school girls, some of them athletes, but none of them currently involved in contact sports, to serve as a control group.

These girls completed the pointing and anti-pointing tasks on the iPad after a full day of school.

Then the soccer players took their turns with the iPads.

It turned out, that the soccer players were not as adept at the anti-point test. As a group, their responses were slightly but significantly slower, suggesting some degree of cognitive impairment.

What is more, the more times a girl had headed the ball in the immediately preceding practice, the worse her scores were on the anti-point test.

Wondering whether the effects might, potentially, be cumulative, the researchers then re-ran their analysis, using information about how many years each soccer player had participated in the sport and also how many hours per week she currently practiced.

They found that the more years a girl had played, the slower she tended to be on the anti-point test.

Similarly, the more hours per week a girl played, the worse she performed on the anti-point test.

These results, although troubling, are not cause for panic among the parents of soccer-playing girls, Dr. Sereno said. The study was small, involving just one team, one practice, one age group and one gender. And the differences in test scores were slight, although statistically significant. On a practical level, none of the players were experiencing academic problems at school.

More important, it may be that any effects from heading are transient. “We didn’t re-test the girls,” Dr. Sereno said. Maybe, after a day or even several hours away from the field, the players’ scores would have matched those of the non-soccer players, she said, although the finding that the girls who had played the most years scored the worst “is a bit concerning.”

For now, then, the primary takeaway of her study would seem to be that far more study is needed on the effects of heading and other seemingly minor impacts to the head during sports. “At this point,” she said, “we don’t know the risks” to cognitive function, “or if there are risks.”

She and her colleagues are planning a series of additional iPad-based studies of other age groups and players in other sports, including football. She expects to have results available soon.